Densification behaviour and mechanisms of synthetic hydroxyapatites

Starting from Ca(OH)(2) and H3PO4 hydroxyapatite powders with three differe nt crystallinity degrees have been prepared and characterized. Densificatio n extent and mechanisms were studied through dilatometric measurements in i sothermal regime in the range of temperature 750-1250 degreesC: the influen ce of different powder features (including the effect of calcination treatm ent) have been evaluated. Powder characterized by the lowest crystallinity degree has the highest densification extent overlapping phenomena occurring during the sintering treatments are responsible for unexpectedly low value s found for the shrinkage rate, which can easily lead to a misidentificatio n of the rate controlling mechanism. An interpretation of the densification mechanism, consistent with all experimental findings, is proposed. (C) 200 0 Elsevier Science Ltd. All rights reserved.